In the business software industry, 3-tier-solutions are convenient. Usually, such solutions comprise user-interface systems in a first layer, business application systems in a second layer, and database systems in a third layer (“system” hereinafter left out). Examples for 3-tier-solutions are the well-known software solutions, such as the R/3 and mySAP.com solution that are commercially available from SAP Aktiengesellschaft, Walldorf (Baden), Germany. For the following discussion, the second and third layers deserve closer attention.
The databases are usually implemented as relational databases that communicate with the applications by predefined and. standardized statements, such as System Query Language (SQL) statements.
Relational databases are well known in the art, information is structured in tables, or relations, in which data values are stored in rows, or tuples, under various column headings.
Technological processes, changing customer demands and other circumstances generate demand to migrate data to other databases. Usually, migrating requires time in that the application does not operate as required.
To copy database and/or applications to another location is possible in a short amount of time as long as the structure of the data remains unchanged. Data restructuring requires more time.
However, the acceptance of a business application depends, among other things, on its availability. Customers that appreciate the database services of a patent office do not worry about non-availability during night hours. But there are many other systems that do allow non-availability, as a practical matter, only during certain times of a year, such as during certain holidays. In other words, many business application systems should ideally be available 24 hours a day, 365 days a year.
From a relational database, information is retrieved by a query. When information is to be updated, inserted or deleted from the database by a so-called transaction, at least one table needs to be modified. There are several approaches to deal with database maintenance.
For the discussion of prior art systems, the following references are useful: U.S. Pat. No. 6,141,664; U.S. Pat. No. 6,122,630; U.S. Pat. No. 6,205,451; U.S. Pat. No. 5,893,119; and U.S. Pat. No. 6,006,216.
In any case, there is a technical task to reduce the so-called system downtime during updating the system.